1. Field of the Invention
The present invention relates to a mechanism for retaining a bead with a filler.
2. Description of the Related Art
As a conventional mechanism for retaining a bead with a filler, for example, the mechanism disclosed in JP-Application Laid-Open No. 1-190438 is well known. The mechanism comprises: a ring body, a plurality of extending/retracting means which are separately provided at the ring body in the circumferential direction thereof. An arc-shaped retaining body is provided at each of the extending/retracting means and which can retain a bead with a filler. A driving means applies driving force to the extending/retracting means and operates synchronously these extending/retracting means so as to move and extend/retract the retaining body in the radial direction of the ring body. Each of the extending/retracting means includes a linear guide which is mounted to the ring body and a movable rod which is movably supported by the linear guide in the radial direction of the ring body, and the radially extending line thereof intersects the central axis of the ring body, with the inner end portion thereof being provided with the retaining body.
In a case in which a bead with a filler is retained by such mechanism, the movable rod of each of the extending/retracting means is moved by the driving means inwardly in the radial direction of the ring body. Accordingly, the retaining bodies reach the predetermined positions in the radial direction of the ring body and all of the arc-shaped retaining bodies are positioned on the same circle which centers around the central axis of the ring body. Thereafter, a bead with a filler is supplied to and retained by the retaining body. Then, the bead with the filler retained as such is delivered from the retaining body to a tire forming drum. After such delivery, in order to prevent a case in which the retaining body interferes with the filler whose radius is larger than that of the bead, the movable rod of each of the extending/retracting means is moved by the driving means outwardly in the radial direction of the ring body. The retaining body is moved further outward in the radial direction of the ring body than the outer end of the filler in the radial direction thereof.
However, in such conventional mechanism for retaining a bead with a filler, the linear guide itself is expensive. Moreover, because the linear guide has large sliding resistance, it is necessary to use expensive driving means which can generate large driving force. As a result, a drawback arises in that cost of equipment becomes high. Further, in order to operate smoothly the aforementioned linear guide and movable rod, the retaining mechanism must be assembled and adjusted at high accuracy. Additionally, there is a drawback in that high accuracy must be maintained for a long period of time. Further, in the aforementioned retaining mechanism, when the retaining body is moved outermost in the radial direction of the ring body, the outer portion of the movable rod in the radial direction of the ring body projects from the ring body outwardly in the radial direction thereof by a large amount. Thus, a drawback arises in that the entire retaining mechanism becomes large.